Numerical research on aeroacoustics of supersonic single/twin rectangular jets

Rectangular nozzles are increasingly valued in military aircraft design due to their excellent thrust vectoring control and stealth performance. However, twin jet coupling remains an attractive aero-acoustic problem as its noise characteristics and sound generation mechanism are still not well understood. In this paper, numerical simulations of supersonic under-expanded single/twin rectangular jets are conducted. High-precision numerical schemes and implicit large eddy simulation methods are used, and the predicted flow and acoustic characteristics of the single jet show good agreement with the experimental results. The findings indicate that when twin jet spacing is 3.5h, the interaction between twin jets has little impact on the internal structure and shear layer development of the jets. There are significant differences in the overall sound pressure level distribution and the noise directivity between single and twin jets. Compared with the single jet, twin jets exhibit a slightly reduced screech frequency, and a significantly increased intensity. Fourier mode decomposition and spectral proper orthogonal decomposition are employed to extract coherent structures in the flow field. A helical mode is revealed in the single jet, while in the twin jets, the mode switches to a flapping mode along the minor axis with the two jets oscillating in phase. Modal analysis further highlights the relationship between changes in screech frequency and intensity and the shift in the sound source location.